Superconducting cable joint structure

ABSTRACT

A superconducting cable joint structure is a structure used to joint together superconducting cables used at cryogenic temperature or to joint together a terminal of the superconducting cable and a normal conducting cable, and it includes a joint insulation layer arranged radially outer than a portion connecting the superconducting cables&#39; respective conductors together or the superconducting cable&#39;s conductor and the normal conducting cable&#39;s conductor together, and at least one coolant path provided at the joint insulation layer to cool the portion connecting the conductors together. The cable cores can have their connection prevented from generating heat to have an increased temperature.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to superconducting cablejoint structures and more specifically to effectively preventing aconductor connection from overheating in jointing and thus connecting anend of a core of a superconducting cable to a counterpart conductor.

[0003] 2. Description of the Background Art

[0004] Currently, cities and the like have a tendency to consumeincreasing amounts of power, and accordingly require larger undergroundpower transmission capacities. Accordingly, a superconducting cableallowing as large a current density as approximately 100 times that of aconventional cable is being developed. This superconducting cable is, asdisclosed for example in Japanese Patent Laying-Open No. 2002-140943,structured such that a plurality of cable cores having a superconductorpass through an external casing's internal space having liquid nitrogenor the like flowing therethrough to serve as a coolant layer.

[0005] To lay the aforementioned superconducting cable underground, itis necessary to connect together such superconducting cables of aprescribed length. Currently, however, there has not been a methodproposed to suitably joint a superconducting cable currently beingstudied. Japanese Patent Laying-Open No. 7-335358 discloses jointing andthus connecting together a conventional, non-superconducting power cableand a counterpart power cable. More specifically, as shown in FIG. 11,power cables 1 have their respective ends with their respective, exposedconductors 2 abutting against each other and connected together by aconductor connection sleeve 3 externally fitted thereon and furthermorethey are externally, circumferentially surrounded by an oil impregnatedpaper.

[0006] However, if the method of jointing conventional power cables 1together, as shown in FIG. 11, is employed to joint and thus connecttogether cores of superconducting cables, respectively, conductorconnection sleeve 3, which is a normal conductor, and a superconductorwill be connected together. This provides an increased value inresistance at a portion connecting the normal conductor and thesuperconductor together. As a result, an increased quantity of heat isgenerated and a coolant surrounding the cable cores may bubble and as aresult destroy a coolant impregnated paper, and to maintain the cable'ssuperconducting property a refrigerator having a large capacity isrequired. Furthermore, the increased resistance at the portionconnecting the conductor connection sleeve of the normal conductor andthe superconductor together, contributes to a reduced current capacityof the superconducting cable in its entirety.

SUMMARY OF THE INVENTION

[0007] The present invention contemplates jointing and thus connectingtogether cores of superconducting cables, respectively, while preventinga connection from generating heat to increase temperature and alsoallowing the connection to provide a reduced current resistance and thusgenerate a reduced quantity of heat.

[0008] The present invention in one aspect provides a structure jointingtogether superconducting cables used at cryogenic temperature, orjointing together a terminal of the superconducting cable and a normalconducting cable, the structure including: a joint insulation layerprovided at an external circumference of a conductor connectionconnecting together conductors of the superconducting cables,respectively, or connecting together the conductor of thesuperconducting cable and a conductor of the normal conducting cable;and at least a single coolant path provided at the joint insulationlayer to cool the conductor connection. Note that in the presentinvention the normal conducting cable also includes a lead rod, anelectric current lead and other similar connection rods and conductordrawing rods and other similar metal rods.

[0009] The joint insulation layer is provided with a coolant pathreceiving and passing a coolant. When the conductor connection generatesheat the coolant flowing through the coolant path can remove the heat toprevent the conductor connection from overheating.

[0010] Preferably in the present structure the superconducting cable hasan external casing and a cable core inserted into an internal space ofthe external casing. The cable core has a former formed of a longfilament, a superconducting layer provided on a radially outer surfaceof the former, and an insulation layer arranged radially outer than thesuperconducting layer. The internal space serves as a coolant layerpassing a coolant therethrough, the coolant layer directly contactingthe joint insulation layer, with coolant path passing the coolant of thecoolant layer.

[0011] Thus a coolant used to cool a cable core having a superconductinglayer serving as the conductor can also be passed into a coolant path ofa joint insulation layer.

[0012] Preferably in the present structure the joint insulation layer isformed of coolant impregnated papers deposited in layers. The jointinsulation layer formed of coolant impregnated layers can also be usedto directly cool the conductor connection. This can interact with theeffect achieved by the coolant path to cool the conductor connection,achieving a synergistic effect.

[0013] Preferably the present structure further includes a conductorconnection sleeve arranged at the conductor connection andcompression-connected to a radially other surface of the conductors ofthe superconducting cables arranged to abut against each other or aradially outer surface of the conductor of the superconducting cable andthe conductor of the normal conducting cable arranged to abut againsteach other. Conductors abutting against each other that are connectedtogether by an externally fitted conductor connection sleeve can havetheir joint maintained mechanically stably.

[0014] Preferably in the present structure the coolant path has aradially inner opening along a radially outer surface of the conductorconnection sleeve to allow the radially outer surface to directlycontact the coolant.

[0015] Opposite conductors are connected together by an externallyfitted conductor connection sleeve, and the sleeve generates heat.However, a coolant path having a radially inner opening communicatingwith the sleeve can pass a coolant through the radially inner opening tocool the sleeve's radially outer surface directly and hence moreefficiently to effectively prevent the sleeve from overheating.

[0016] Preferably in the present structure the coolant path has aninclined path connecting the radially inner opening to a radially outeropening of the coolant path.

[0017] If the coolant path forms a right angle relative to thelongitudinal direction of the cable and thus provides a significantlyangled portion a voltage applied to the conductor may increase anelectric field created at a boundary of the insulation layer and thecoolant path, and an equipotential surface of the electric field createdtherearound may not be maintained at the significantly angled portion inparallel, resulting in the electric field exceeding a critical value.The coolant path that is inclined can effectively contribute to analleviated electric field created at a boundary plane of the insulationlayer and the coolant path.

[0018] Furthermore, the joint insulation layer may be formed of aninsulating resin molding provided with a coolant path. In other words,it is not required to be coolant impregnated papers deposited in layers.

[0019] Preferably in the present structure the superconducting cable andthe normal conducting cable are connected together via the conductorconnection such that the conductor protruding from the normal conductingcable and a conductor of the superconducting cable are connectedtogether via the conductor connection circumferentially provided withthe joint insulation layer, and the coolant path is arranged at aninterface of an end surface of the joint insulation layer and an outerend surface of the normal conducting cable.

[0020] A normal conducting cable's conductor and a superconducting cableare connected together and a portion such that the normal conductingcable and the joint insulation layer have an interface provided with acoolant path. The coolant path can be readily formed. Furthermore whenthe conductor connection generates heat, the heat can be diffused to thecoolant path to prevent the conductor connection from overheating.

[0021] Preferably, the normal conducting cable provides a securingportion of insulator formed of epoxy resin presenting high heatresistance, a small percentage of contraction (high dimensionalstability) as it cures, and an excellent adhesive property.

[0022] Preferably in the present structure the interface is inclinedrelative to a longitudinal direction of the cable core and provided withthe coolant path.

[0023] If the coolant path forms a right angle relative to thelongitudinal direction of the cable and thus provides a significantlyangled portion a voltage applied to the conductor may increase anelectric field created at a boundary of the insulation layer and thecoolant path, and an equipotential surface of the electric field createdtherearound may not be maintained at the significantly angled portion inparallel, resulting in the electric field exceeding a critical value.The coolant path that is provided at an inclined plane can effectivelycontribute to an alleviated electric field at the boundary.

[0024] If the coolant path forms a right angle relative to thelongitudinal direction of the cable and thus provides a significantlyangled portion an equipotential surface of an electric field createdtherearound by a current flowing through the conductor may not bemaintained at the significantly angled portion in parallel, resulting inthe electric field exceeding a critical value. The coolant path that isprovided at an inclined interface can facilitate in the joint insulationlayer an electric field's equipotential to be maintained substantiallyparallel to prevent electric field from increasing.

[0025] The present invention in another aspect provides asuperconducting cable joint structure jointing together superconductingcables used at cryogenic temperature, or jointing together a terminal ofthe superconducting cable and a normal conducting cable. The structureincludes: a conductor connection allowing the conductor cables to havetheir respective conductors abutting against each other and connectedtogether, or allowing the superconducting cable and the normalconducting cable to have their respective conductors abutting againsteach other and connected together; a conductor connection sleevecompression-connecting a circumference of the conductor connection; asuperconducting wire provided on a radially outer surface of theconductor connection sleeve or buried internal to the conductorconnection sleeve to alleviate generation of heat; and a jointinsulation layer provided at an outer circumference of the conductorconnection sleeve or the superconducting wire.

[0026] As the superconducting wire connected to the conductor connectionsleeve's outer or inner surface is significantly smaller in resistancethan the sleeve, a current from a conductor (a superconductor) of asuperconducting cable tends to flow through the wire rather than thesleeve. A reduced amount of heat can thus be generated. Furthermore atthe conductor connection a current tends to flow through thesuperconducting wire, rather than the conductor connection sleeve, asthe wire is has smaller resistance than the sleeve. The superconductingcable as seen in entirety can be prevented from having reduced currentcapacity.

[0027] The superconducting wire has opposite ends electrically connectedto the conductor of each of two the superconducting cables to beconnected together, or the conductor of the superconducting cable andthe conductor of the normal conducting cable to be connected together.

[0028] Thus a superconducting wire small in resistance can directlycrosslink connection of conductors of superconducting cables,respectively, to alleviate generation of heat and the conductorconnection sleeve can maintain a steady joint.

[0029] Suitably the superconducting wire is arranged on the conductorconnection sleeve at a radially outer surface longitudinally or spirallywound therearound and soldered thereto.

[0030] The present invention in still another aspect provides asuperconducting cable joint structure jointing together superconductingcables used at cryogenic temperature, or jointing together a terminal ofthe superconducting cable and a normal conducting cable. The structureincludes: a conductor connection allowing the conductor cables to havetheir respective conductors abutting against each other, welded andelectrically connected together, or allowing the superconducting cableand the normal conducting cable to have their respective conductorsabutting against each other, welded and electrically connected together;a superconducting wire arranged on a circumference of the conductorconnection longitudinally or wound therearound to alleviate generationof heat; and a joint insulation layer arranged radially outer than thesuperconducting wire.

[0031] As the superconducting wire connected to the conductor connectionsleeve's outer or inner surface is significantly smaller in resistancethan the sleeve, a current from a superconducting layer of a cable coretends to flow through the wire rather than the sleeve. A reduced amountof heat can thus be generated. Furthermore at the conductor connection acurrent tends to flow through the superconducting wire, rather than theconductor connection sleeve, as the wire is has smaller resistance thanthe sleeve. The superconducting cable as seen in entirety can beprevented from having reduced current capacity.

[0032] Preferably in the present structure the joint insulation layerhas at least one coolant path. This is further preferable as an approachagainst heat, as such can interact with the effect of alleviatinggeneration of heat, achieving a synergistic effect through the coolantpath to diffuse heat.

[0033] The superconducting cable and the normal conducting cable havethe conductor connection such that the superconducting cable has aconductor protruding therefrom, the superconductor and the conductor ofthe superconducting cable are connected together via the conductorconnection with the joint insulation layer arranged radially outer thanthe conductor connection, and furthermore, an end surface of the jointinsulation layer and an outer end surface of the normal conducting cableare connected together forming an interface and the interface isprovided with a coolant path. This is preferable as such allows thecoolant path to be readily formed and can also prevent the conductorconnection from overheating.

[0034] The superconducting cable includes a cable core having a formerformed of a long filament, a superconducting layer spirally wound aroundthe former's circumference in multiple layers, and an insulation layerradially outer than the superconducting layer. The cable core has aterminal with the former and the superconducting layer exposed stepwise,and the conductor connection sleeve has a radially inner or outersurface with a superconducting wire buried therein to alleviategeneration of heat and connected to the stepwise exposed former andsuperconducting layer. The superconducting layer stepwise exposed allowsthe conductor connection sleeve to establish steady electricalconnection with each layer's superconducting layer.

[0035] The above structure, as specifically configured, has more thanone cable core interconnected, each having a shield layer with asuperconducting wire arranged radially outer than the insulation layer,and a protection layer formed of an insulator and arranged radiallyouter than the shield layer, and the superconducting layer of the cablecore and the superconducting layer of another cable core or theconductor of the normal conducting cable are connected together via theconductor connection covered with the joint insulation layer.

[0036] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In the drawings:

[0038]FIG. 1A is a cross section of the present superconducting cable inan embodiment, FIG. 1B is a perspective view of a cable core, and FIG.1C is a perspective view of a superconductor;

[0039]FIG. 2A is a longitudinal cross section illustrating a manner ofconnecting the cores of the superconducting cables of the firstembodiment, and FIG. 2B is an orthogonal cross section thereof;

[0040]FIGS. 3-5 are longitudinal cross sections illustrating manners ofconnecting the cores of the superconducting cables in second to fourthembodiments, respectively;

[0041]FIG. 6 is a cross section illustrating an exemplary variation ofthe fourth embodiment;

[0042]FIG. 7 is a longitudinal cross section illustrating a manner ofconnecting the cores of the superconducting cables in a fifthembodiment;

[0043]FIG. 8 is a cross section illustrating an exemplary variation ofthe fifth embodiment;

[0044]FIGS. 9 and 10 are longitudinal cross sections illustratingmanners of connecting the cores of the superconducting cables in sixthand seventh embodiments, respectively; and

[0045]FIG. 11 is a cross section of a conventional example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] The present invention in embodiments will now be described withreference to the drawings.

[0047] With reference to FIG. 1A, the present embodiment provides asuperconducting cable 100 including, as seen radially outward, an innercorrugated pipe 15, an insulation layer 16, an outer corrugated pipe 17and an anti-corrosive layer 18 deposited in layers to form a cylinder toform an external casing 70 serving as an insulation pipe. Externalcasing 70 has an internal space 71 serving as a coolant layer R and alsopassing three cable cores 10 therethrough. Inner and outer corrugatedpipes 15 and 17 are corrugated cylinders formed of stainless steel andanti-corrosive layer 18 is formed for example of polyvinyl chloride(PVC). Coolant layer R uses a coolant of liquid nitrogen, liquid heliumor the like.

[0048] Cable core 10, as shown in FIGS. 1A and 1B, includes a former 11formed of copper wires twisted together and placed at the center of thecore, a superconducting layer 12 formed of a superconductor spirallywound around former 11, and an insulation layer 13, a shield layer and aprotection layer (not shown) wound around an outer circumference ofsuperconducting layer 12.

[0049] Former 11 is formed of a large number of copper wires having astrand insulated that are twisted together to maintain the cable core 10mechanical characteristics (rigidity, bending characteristic, and thelike) and also reduce a loss of eddy current in the former. Furthermore,as former 11 has an outer circumference with superconducting layer 12wound therearound and superconducting layer 12 is significantly lower inresistance, a current tends to flow through superconducting layer 12rather than former 11. It should be noted, however, that if an eddycurrent flows and a critical current Ic is exceeded, superconductinglayer 12 will be increased in resistance and former 11 will also pass acurrent and function as a bypass for safety. Former 11 may be formed ofmetal other than copper.

[0050] Superconducting layer 12 is, as shown in FIG. 1C, is formed of awire in the form of a tape formed of bismuth (Bi)-2223, superconductingfilaments 12 b and a silver 12 a (or a silver alloy) covering thefilaments. Superconducting filament 12 b may be formed of ceramic forexample of yttrium oxide, thallium oxide, bismuth oxide.

[0051] Insulation layer 13 is formed of a polypropylene laminated paper(PPLP) formed of a polypropylene film at least having one surface with akraft paper bonded thereon. Insulation layer 13 is impregnated with acoolant and it is in a low temperature insulation system. Alternatively,insulation layer 13 may be a paper formed for example of polyethylenefilm, polypropylene film and the like combined together.

[0052] Shield layer 14 has a configuration similar to that ofsuperconducting layer 12 and passes a current in a direction opposite tosuperconducting layer 12 to cancel a magnetic field.

[0053] Superconducting cable 100 has cable core 10 jointed and connectedin a first embodiment, as will be described hereinafter.

[0054] First Embodiment

[0055] With reference to FIG. 2A, the present embodiment provides asuperconducting cable joint structure 52. More specifically, twoopposite cable cores 10 have their respective formers 11 andsuperconducting layers 12 each exposed stepwise so that they can beconnected to conductor connection sleeve 19. Formers 11 abuts againsteach other and conductor connection sleeve 19, formed in a cylinder ofmetal (e.g., copper, aluminum or the like), is externally fitted andconnected to establish a conductor connection 22.

[0056] Conductor connection sleeve 19 and superconducting layer 12 areelectrically connected for example with solder, and conductor connectionsleeve 19 and former 11 are compression-connected.

[0057] Conductor connection sleeve 19 is covered with first and second,coolant impregnated papers 20A and 20B wound therearound to serve as ajoint insulation layer 20. As well as insulation layer 13, the first andsecond coolant impregnated papers 20A and 20B may also be formed ofpolypropylene laminated paper (PPLP) formed of a polypropylene film atleast having one surface with a kraft paper bonded thereon, or may bekraft paper.

[0058] More specifically, as shown in FIG. 2A, conductor connectionsleeve 19 has wound therearound the first coolant impregnated paper 20Adivided in two as seen longitudinally, and, as shown in FIG. 2B, thefirst coolant impregnated paper 20A has a radially outer surface withspacers 21 arranged thereon circumferentially and spaced, and thereonthe second coolant impregnated paper 20B is wound to form jointinsulation layer 20 having a coolant path S.

[0059] Note that joint insulation layer 20 has an end with a sidesurface 20 c inclined so that it does not form a right angle relative tothe longitudinal direction of cable core 10 and is thus smoothlyadjacent to the cable core.

[0060] If side surface 20 c forms a right angle relative to thelongitudinal direction of the cable and thus provides a significantlyangled portion a voltage applied to superconducting layer 12 mayincrease an electric field created at a boundary of joint insulationlayer 20 and side surface 20 c, and an equipotential surface of theelectric field created therearound may not be maintained at thesignificantly angled portion in parallel, resulting in the electricfield exceeding a critical value. Joint insulation layer 20 having anend with side surface 20 c smoothly adjacent to cable core 10 caneffectively contribute to an alleviated electric field at the boundary.

[0061] Furthermore, as shown in FIG. 2A, coolant path S has a horizontalportion Sa and an inclined portion Sb. Horizontal portion Sa has an endcommunicating with coolant layer R and inclined portion Sb also has anend adjacent to an outer surface of conductor connection sleeve 19.

[0062] In other words, coolant path S has inclined path Sb connecting aradially inner opening S1 of coolant path S and a radially outer openingS2 of coolant path S. Radially inner opening S1 is positioned atconductor connection sleeve 19 along a radially outer surface 19 a,which directly contacts the coolant. Portion Sb is inclined relative tothe longitudinal direction of cable core 10, rather than perpendicularthereto, for the same reason as side surface 20 c is inclined.

[0063] Thus, opposite cable cores 10 have their respective conductivelayers 12 connected together by a normal conductor, or conductorconnection sleeve 19, externally fitted thereon. Although sleeve 19generates heat, a coolant of coolant layer R corresponding to internalspace 71 of inner corrugated pipe 15 can flow into coolant path S formedin joint insulation layer 20 and the heat generated at sleeve 19 can bediffused to coolant layer R through convection of the coolant in coolantpath S to prevent sleeve 19 from overheating.

[0064] Note that while in the present embodiment, as shown in FIG. 2B,more than one coolant path S are circumferentially arranged, any numberthereof may be arranged. For example, only a single coolant path may bearranged. Furthermore, spacer 21 is suitably interposed internal to theinsulation layer formed of coolant impregnated papers 20A and 20B woundin layers. However, it may be arranged between a radially outer surfaceof cable core 10 and joint insulation layer 20. Furthermore, jointinsulation layer 20 may be an insulation resin molding.

[0065] Second Embodiment

[0066] With reference to FIG. 3, the present embodiment differs from thefirst embodiment in that while the present embodiment provides asuperconducting cable joint structure 53 including a joint insulationlayer 20′ having a coolant path S′ extending along cable core 10, asseen longitudinally, and communicating at a portion adjacent toconductor connection sleeve 19.

[0067] Coolant path S′ has a horizontal portion Sa′ communicating an endSf′ to coolant layer R, an inclined portion Sb′ communicating withhorizontal portion Sa′ and having an end adjacent to conductorconnection sleeve 19 at radially outer surface 19 a, a horizontalportion Sd′ communicating an end Sg′ to coolant layer R, an inclinedportion Se′ communicating with horizontal portion Sd′ and having an endadjacent to sleeve 19 at surface 19 a, and a communication portion Sc′allowing opposite inclined portions Sb′ and Se′ to have their respectiveends communicating with each other.

[0068] More specifically, conductor connection sleeve 19 has woundtherearound the first coolant impregnated paper 20A divided in two asseen longitudinally. The first coolant impregnated paper 20A is thenprovided on a radially outer surface thereof with spacers arrangedcircumferentially and spaced. Thereon a second coolant impregnated paper20B′ is wound. Joint insulation layer 20′ having coolant path S′ is thusformed. In doing so, also arranging spacers between the ends of inclinedportions Sb′ and Se′ on an outer surface of sleeve 19 such that thespacers are circumferentially arranged and are also spaced, and windingthe second coolant impregnated paper 20B′ therearound allowscommunication portion Sc′ to be formed horizontal and adjacent to sleeve19 at surface 19 a.

[0069] The above arrangement allows a coolant present in coolant layer Rexternal to joint insulation layer 20′ to flow into coolant path S′ atone end Sg′ and flow out at the other end Sf′. The coolant can thuscirculate through coolant path S′ to more efficiently cool sleeve 19.

[0070] The remainder of the configuration of the present embodiment issimilar to that of the configuration of the first embodiment.

[0071] Third Embodiment

[0072] In the present embodiment will be described a structure jointingtogether a terminal of a superconducting cable and a resin unit employedto secure a normal conducting cable.

[0073] With reference to FIG. 4, the present embodiment differs from thefirst embodiment in that the present embodiment provides asuperconducting cable joint structure 54 connecting the superconductingcable 100 cable core 10 to a conductor 31 of a resin unit 33 employed tosecure a normal conducting cable to an external member.

[0074] In resin unit 33 conductor 31 formed of aluminum or copper issurrounded by a securing portion of insulator 32 formed of epoxy resinin the form of a rhomboid as seen in cross section. Securing portion ofinsulator 32 has an end with conductor 31 protruding and thus exposed,and having an end, connection portion 31 a, which is externally fittedon and thus connected to superconducting layer 12 of cable core 10.

[0075] An outer surface of conductor connection sleeve 19 and a sidesurface 32 a of the end of securing portion of insulator 32 are coveredwith coolant impregnated papers 30A and 30B wound therearound to form ajoint insulation layer 30. Joint insulation layer 30 and normalconducting cable 33 have an interface 33 a inclined relative to thelongitudinal direction of cable core 14 and provided with a coolant pathS1.

[0076] More specifically, side surface 32 a is provided with spacedspacers (not shown) along a circumference of cable core 10, and thefirst coolant impregnated paper 30A is wound around and thus covers aprotrusion of conductor 31 serving as conductor connection 22. Then thefirst coolant impregnated paper 30A is also externally,circumferentially provided with spaced spacers (not shown), and thereonthe second coolant impregnated paper 30B is wound to form jointinsulation layer 30. In other words, joint insulation layer 30 andsecuring portion of insulator 32 have an interface provided with thefirst coolant path S1 communicating with coolant layer R, and jointinsulation layer 30 is internally provided with the second coolant pathS2 communicating the first coolant path S1 to the conductor 31 end,connection portion 31 a.

[0077] The second coolant path S2 has a horizontal portion S2 bcommunicating with the first coolant path S1 and an inclined portion S2a adjacent to conductor 31 at end, connection portion 31 a. Note thatwhile the first coolant path S1 has an end communicating with conductor31, it is only required to at least communicate with the second coolantpath S2. It is not a requirement that the first coolant path S1communicate with conductor 31.

[0078] Thus coolant layer R external to cable core 10 can have a coolantflowing through the first coolant path S1 into the second coolant pathS2 so that heat generated at end, connection portion 31 a of conductor31 serving as conductor connection 22 can be diffused through the firstand second coolant paths S1 and S2 to coolant layer R to preventconductor connection 22 from overheating.

[0079] While securing portion of insulator 32 is suitably formed ofepoxy resin when heat resistance, dimensional stability and adhesion areconsidered, it is not limited to a specific material as long as itexhibits high heat resistance, provides a small percentage ofcontraction (or high dimensional stability) as it cures, and anexcellent adhesive property. Furthermore, the resin unit 32 conductor 31may be a superconductor.

[0080] Fourth Embodiment

[0081] With reference to FIG. 5, the present embodiment provides asuperconducting cable joint structure 55 including conductor connectionsleeve 19 having a radially outer surface with a superconducting wire 41spirally wound therearound and soldered thereto to alleviate generationof heat. A joint insulation layer 40 is not provided with a coolantpath. Superconducting wire 41 is similar in configuration tosuperconducting layer 12 shown in FIG. 1C and it may be wound densely orsparsely. Superconducting wire 41 has opposite ends 41 a abuttingagainst cable core 10 at superconducting layer 12. Thus superconductingwire 41 has the opposite ends electrically connected to former 11 ofeach of two superconducting cables 100 connected.

[0082] Thus, opposite cable cores 10 have their respectivesuperconducting layers 12 and formers 11 connected by externally fittedconductor connection sleeve 19 that has a radially outer surface withsuperconducting wire 41 connected thereto. As superconducting wire 41 issmaller in resistance than conductor connection sleeve 19, a currenttends to flow through wire 41 rather than sleeve 19. Sleeve 19 can thusgenerate a reduced quantity of heat.

[0083] While in the present embodiment superconducting wire 41 isspirally wound, wire 41 may simply be arranged on conductor connectionsleeve 19 at radially outer surface 19 a longitudinally (or in thelongitudinal direction of cable core 10). Alternatively, wire 41 maysimply be buried in conductor connection sleeve 19. Furthermore, wire 41is not required to have an end in contact with superconducting layer 12.Furthermore, while in the present embodiment wire 41 is soldered tolayer 12, wire 41 may simply be buried as joint insulation layer 40 iswound. Alternatively, wire 41 may be arranged radially inner than sleeve19.

[0084] The remainder of the configuration of the present embodiment issimilar to that of the configuration of the first embodiment.

[0085] While the present embodiment has been described in conjunctionwith superconducting cable joint structure 55 employed to connectsuperconducting cables together, the present invention is alsoapplicable to a superconducting cable joint structure employed toconnect a superconducting cable and a normal conducting cable together.

[0086] Furthermore, with reference to FIG. 6, the present embodimentprovides another superconducting cable joint structure 56, in which afirst coolant impregnated paper 40A divided in two as seenlongitudinally is wound around and thus covers superconducting wire 41arranged on conductor connection sleeve 19 at radially outer surface 19a and an outer surface of cable core 10 adjacent thereto. Furthermore,the first coolant impregnated paper 40A is externally, circumferentiallysurrounded by spaced spacers (not shown) and on the spacers a secondcoolant impregnated paper 40B is wound. Thus, a joint insulation layer40′ has coolant path S allowing external coolant layer R to communicatewith superconducting wire 41 arranged on conductor connection sleeve 19at radially outer surface 19 a.

[0087] Thus a coolant external to joint insulation layer 40′ can flowsinto coolant path S. If conductor connection sleeve 19 andsuperconducting wire 41 generate heat, coolant path S allows the heat tobe diffused to the coolant. This can provide a synergistic, effectiveapproach against heat as it interacts with the effect of reducing aquantity of heat that is attributed to providing sleeve 19 with wire 14.

[0088] Fifth Embodiment

[0089] With reference to FIG. 7, the present embodiment provides asuperconducting cable joint structure 57. More specifically, oppositecable cores 10 having their respective formers 11 abutting against eachother are welded and thus connected together. Furthermore, former 11 andsuperconducting layer 12 have an outer surface with a superconductingwire 51 spirally wound therearound and soldered or the like to layer 12to establish electrical connection. Furthermore, radially externalthereto is a coolant impregnated paper wound therearound to form a jointinsulation layer 50.

[0090] Thus, opposite cable cores 10 have their respectivesuperconducting layers 12 electrically connected by superconducting wire51. The electrical connection can be achieved with electrical resistancehaving a small value so that the connection can generate a reducedquantity of heat. Furthermore, while superconducting wire 51 used toprovide electrical connection has small rigidity, formers 11 havingsufficient rigidity can be welded and connected together, and theconnection can have constantly maintained strength.

[0091] Note that while in the present embodiment superconducting wire 51is spirally wound, wire 51 may simply be placed on superconducting layer12 and former 11 at an outer surface longitudinally. Furthermore, whilein the present embodiment wire 51 is soldered to layer 12, wire 51 maysimply be buried by a force of joint insulation layer 50 woundtherearound.

[0092] The remainder of the configuration of the present embodiment issimilar to that of the configuration of the first embodiment.

[0093] Furthermore, with reference to FIG. 8, the present embodimentprovides another superconducting cable joint structure 58. Morespecifically, superconducting wire 51 and cable core 10 adjacent theretohave an external surface covered with a first coolant impregnated paper50A divided in two as seen longitudinally and wound therearound. Thefirst coolant impregnated paper 50A is externally, circumferentiallyprovided with spaced spacers (not shown), and on the spacers a secondcoolant impregnated paper 50B is wound. Thus a joint insulation layer50′ has coolant path S allowing external coolant layer R to communicatewith superconducting wire 51.

[0094] Thus, a coolant external to joint insulation layer 50′ can flowinto coolant path S. If superconducting wire 51 generates heat, coolantpath S allows the heat to be diffused to the coolant. This can provide asynergistic, adequate approach against heat as it interacts with theeffect of reducing a quantity of heat that is attributed to employingsuperconducting wire 51.

[0095] Sixth Embodiment

[0096] With reference to FIG. 9, the present embodiment differs from thethird embodiment, as follows: the present embodiment provides asuperconducting cable joint structure 59, in which a securing resin unit33′ corresponding to a normal conducting cable has a conductor 60 with asuperconductor 61 spirally wound therearound, and furthermore, the resinunit 33′ superconductor 61 and the cable core 10 superconducting layer12 are connected together by conductor connection sleeve 19 externallyfitted thereon and furthermore having an outer surface withsuperconducting wire 41 spirally wound therearound.

[0097] More specifically in resin unit 33′ conductor 60 formed ofaluminum or copper is surrounded by superconductor 61 spirally woundtherearound and superconductor 61 is also surrounded by securing portionof insulator 32 formed of epoxy resin in the form of a rhomboid as seenin cross section. Securing portion of insulator 32 has an end withconductor 60 and superconductor 61 protruding stepwise.

[0098] Conductor 60 has an end abutting against cable core 10 at former11, and superconductor 61 and superconducting layer 12 are connectedtogether by conductor connection sleeve 19 externally fitted thereon andhaving radially outer surface 19 a with superconducting wire 41 spirallywound therearound, and soldered and thus connected thereto.

[0099] Securing portion of insulator 32 has an end with side surface 32a provided with spacers (not shown) arranged circumferentially andspaced and the first coolant impregnated paper 30A is wound to coverconductor connection sleeve 19 provided with superconducting wire 41.Furthermore, the first coolant impregnated paper 30A is externally,cirumferentially surrounded by spacers (not shown) and thereon thesecond coolant impregnated paper 30 is wound to form joint insulationlayer 30. Thus, joint insulation layer 30 and securing portion ofinsulator 32 have an interface 63 provided with the first coolant pathS1 communicating with coolant layer R and joint insulation layer 30 isinternally provided with the second coolant path S2 communicating thefirst coolant path S1 to superconducting wire 41.

[0100] The remainder of the configuration of the present embodiment issimilar to that of the configuration of the third embodiment.

[0101] Seventh Embodiment

[0102] With reference to FIG. 10, the present embodiment differs fromthe sixth embodiment in that the present embodiment provides asuperconducting cable joint structure 66 in which the securing resinunit 33′ conductor 60 and the cable core 10 former 11 abut against eachother and are welded together, and former 11, superconductor 61 andsuperconducting layer 12 have an external surface with superconductingwire 51 spirally wound therearound and soldered or the like tosuperconducting layer 12, 61 to establish electrical connection.

[0103] Furthermore, as well as in the third and sixth embodiments, thefirst and second coolant impregnated papers 30A and 30B are wound toform joint insulation layer 30 having the second and first coolant pathsS2 and S1.

[0104] The remainder of the configuration of the present embodiment issimilar to that of the configuration of the third embodiment.

[0105] In accordance with the present invention, as apparent from theabove description, a superconducting cable's joint connection hasexternally fitted thereon a joint insulation layer provided with acoolant path so that heat generated at a conductor connection can bediffused by a coolant flowing into the coolant path to prevent theconductor connection from overheating. Furthermore, at the conductorconnection, conductors can be connected together by an externallyfitted, superconducting wire equipped conductor connection sleeve ordirectly by the superconducting wire to allow the joint to generate areduced quantity of heat.

[0106] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A structure jointing together superconductingcables used at cryogenic temperature, or jointing together a terminal ofsaid superconducting cable and a normal conducting cable, the structurecomprising: a joint insulation layer provided at an externalcircumference of a conductor connection connecting together conductorsof said superconducting cables, respectively, or connecting togethersaid conductor of said superconducting cable and a conductor of saidnormal conducting cable; and at least a single coolant path provided atsaid joint insulation layer to cool said conductor connection.
 2. Thestructure of claim 1, wherein: said superconducting cable has anexternal casing and a cable core inserted into an internal space of saidexternal casing; said cable core has a former formed of a long filament,a superconducting layer provided on a radially outer surface of saidformer, and an insulation layer arranged radially outer than saidsuperconducting layer; and said internal space serves as a coolant layerpassing a coolant therethrough, said coolant layer directly contactingsaid joint insulation layer, with coolant path passing the coolant ofsaid coolant layer.
 3. The structure of claim 2, wherein: saidsuperconducting cable has more than one said cable core interconnected,each having a shield layer with a superconducting wire arranged radiallyouter than said insulation layer, and a protection layer formed of aninsulator and arranged radially outer than said shield layer; and saidsuperconducting layer of said cable core and said superconducting layerof another said cable core or said conductor of said normal conductingcable are connected together via said conductor connection covered withsaid joint insulation layer.
 4. The structure of claim 1, wherein saidjoint insulation layer is formed of coolant impregnated papers depositedin layers.
 5. The structure of claim 1, further comprising a conductorconnection sleeve arranged at said conductor connection andcompression-connected to a radially other surface of said conductors ofsaid superconducting cables arranged to abut against each other or aradially outer surface of said conductor of said superconducting cableand said conductor of said normal conducting cable arranged to abutagainst each other.
 6. The structure of claim 5, wherein said coolantpath has a radially inner opening along a radially outer surface of saidconductor connection sleeve to allow said radially outer surface todirectly contact said coolant.
 7. The structure of claim 5, wherein saidcoolant path has an inclined path connecting said radially inner openingto a radially outer opening of said collant path.
 8. The structure ofclaim 5, wherein said cable core has a spirally wound, multilayeredsuperconducting wire, said cable core has a terminal with said formerand said multilayered superconducting layer exposed stepwise, and saidconductor connection sleeve has a radially inner surface connected tosaid former and said multilayered superconducting layer exposedstepwise.
 9. The structure of claim 1, wherein said joint insulationlayer is formed of an insulating resin molding provided with saidcoolant path.
 10. The structure of claim 1, wherein: saidsuperconducting cable and said normal conducting cable are connectedtogether via said conductor connection such that said conductorprotruding from said normal conducting cable and a conductor of saidsuperconducting cable are connected together via said conductorconnection circumferentially provided with said joint insulation layer;and said coolant path is arranged at an interface of an end surface ofsaid joint insulation layer and an outer end surface of said normalconducting cable.
 11. The structure of claim 10, wherein said interfaceis inclined relative to a longitudinal direction of said cable core andprovided with said coolant path.
 12. A structure jointing togethersuperconducting cables used at cryogenic temperature, or jointingtogether a terminal of said superconducting cable and a normalconducting cable, the structure comprising: a conductor connectionallowing said conductor cables to have their respective conductorsabutting against each other and connected together, or allowing saidsuperconducting cable and said normal conducting cable to have theirrespective conductors abutting against each other and connectedtogether; a conductor connection sleeve compression-connecting acircumference of said conductor connection; a superconducting wireprovided on a radially outer surface of said conductor connection sleeveor buried internal to said conductor connection sleeve to alleviategeneration of heat; and a joint insulation layer provided at an outercircumference of said conductor connection sleeve or saidsuperconducting wire.
 13. The structure of claim 12, wherein saidsuperconducting wire has opposite ends electrically connected to saidconductor of each of two said superconducting cables to be connectedtogether, or said conductor of said superconducting cable and saidconductor of said normal conducting cable to be connected together. 14.The structure of claim 12, wherein said superconducting wire is arrangedon said conductor connection sleeve at a radially outer surfacelongitudinally or spirally wound therearound and soldered thereto. 15.The structure of claim 12, wherein said joint insulation layer has atleast one coolant path.
 16. The structure of claim 12, wherein saidsuperconducting cable and said normal conducting cable have saidconductor connection such that said superconducting cable has aconductor protruding therefrom, said superconductor and said conductorof said superconducting cable are connected together via said conductorconnection with said joint insulation layer arranged radially outer thansaid conductor connection, and furthermore, an end surface of said jointinsulation layer and an outer end surface of said normal conductingcable are connected together forming an interface and said interface isprovided with a coolant path.
 17. The structure of claim 12, wherein:superconducting cable has a cable core; said cable core has a formerformed of a long filament, a superconducting layer spirally wound arounda circumference of said former in multiple layers, and an insulationlayer radially outer than said superconducting layer; and said cablecore has a terminal with said former and said superconducting layerexposed stepwise, and said superconducting wire buried in said conductorconnection sleeve at a radially inner surface or a radially outersurface is connected to said former and superconducting layer stepwiseexposed.
 18. The structure of claim 12, wherein: said superconductingcable has more than one said cable core interconnected, each having ashield layer with a superconducting wire arranged at an outercircumference of said insulation layer, and a protection layer formed ofan insulator and arranged at an outer circumference of said shieldlayer; and said superconducting layer of said cable core and saidsuperconducting layer of a plurality of other cable cores or saidconductor of said normal conducting cable are connected together viasaid conductor connection covered with said joint insulation layer. 19.A structure jointing together superconducting cables used at cryogenictemperature, or jointing together a terminal of said superconductingcable and a normal conducting cable, the structure comprising: aconductor connection allowing said conductor cables to have theirrespective conductors abutting against each other, welded andelectrically connected together, or allowing said superconducting cableand said normal conducting cable to have their respective conductorsabutting against each other, welded and electrically connected together;a superconducting wire arranged on a circumference of said conductorconnection longitudinally or wound therearound to alleviate generationof heat; and a joint insulation layer arranged radially outer than saidsuperconducting wire.
 20. The structure of claim 19, wherein said jointinsulation layer has at least one coolant path.
 21. The structure ofclaim 19, wherein said superconducting cable and said normal conductingcable have said conductor connection such that said superconductingcable has a conductor protruding therefrom, said superconductor and saidconductor of said superconducting cable are connected together via saidconductor connection with said joint insulation layer arranged radiallyouter than said conductor connection, and furthermore, an end surface ofsaid joint insulation layer and an outer end surface of said normalconducting cable are connected together forming an interface and saidinterface is provided with a coolant path.
 22. The structure of claim19, wherein: said superconducting cable has more than one said cablecore interconnected, each having a shield layer with a superconductingwire arranged radially outer than said insulation layer, and aprotection layer formed of an insulator and arranged radially outer thansaid shield layer; and said superconducting layer of said cable core andsaid superconducting layer of another said cable core or said conductorof said normal conducting cable are connected together via saidconductor connection covered with said joint insulation layer.